The invention relates to a low-radiation headphone with right and left acoustically irradiating housings associated with the ears of the user. These housings each have an acoustic baffle comprising MU-metal, which is a nickel alloy having high magnetic permeability, in which the dynamic audio transducers are arranged, whereby the acoustic baffle is formed in each case in front of the audio transducer so that it is permeable to sound, and there has a radiation-dissipating zone pointing at the temple of the user. This zone is provided with a higher density of MU-metal than in the remaining area of the acoustic baffle that is permeable to sound.
Low-radiation headphones are known from DE 197 23 644 A1. This known headphone is designed to keep electric and magnetic fields away from the head of the headphone user. These electric and magnetic fields are generated by the audio transducers of the headphone and, in spite of the relatively low power consumption of a headphone, may not be inconsiderable because the audio transducers are arranged close to the head. Headphones with audio transducers in the form of electrostatic controllers typically generate electric fields in the order of magnitude of a few hundred volts per meter. The acoustic irradiation housings of such headphones are substantially screened on all sides. Special attention was paid to screening the area of the acoustic irradiation housing that is located directly adjacent to the head of the user of the headphone. The acoustic baffle of the acoustic irradiation housing is provided for this purpose in the form of a lattice that is coated with MU-metal. An advantageous side effect of this lattice-like design of the acoustic baffle is that the normally required protective cover of the audio transducers can be dispensed with. As an additional screening measure, provision is made in connection with the known headphone that it is provided with a radiation dissipation zone in the form of a MU-metal bridge that is tapered to a point. The tapered MU-metal bridge extends, starting from the edge of a coaxial audio transducer system, to pointing with its tip to the center of the system, and then extends starting from its tip, to the rear in an upwards slanting manner in order to dissipate electric and magnetic radiation in the direction from the temple of the headphone user. The MU-bridge is provided on the top side of the lattice-like acoustic baffle coated with MU-metal, and forms an element that is separated from this wall, so that special installation measures are required. The shape of the bridge tapered to a point was selected in order to interfere as little as possible with the sound dissipation behavior (or property) of the coaxial audio transducer system, because a bridge in such a form is impermeable to sound. For that reason, the high-tone audio transducer seated in the center of the low-medium tone audio transducer is covered by the bridge as little as possible. The MU-metal bridge is formed with a greater material thickness than the coating of the lattice-like acoustic baffle in order to provide an optimal radiation dissipation function.
This known headphone reliably provides its radiation dissipation function within the area of the acoustic baffle of the headphone. However, a substantial expenditure is required for its manufacture.
The present invention provides a low-radiation headphone of the type specified above that can be manufactured at favorable cost while assuring optimal screening against radiation in the area of its acoustic baffles.
Instead of producing the acoustic baffle of each acoustic irradiation housing with a lattice-type structure coated with MU-metal and mounting the radiation dissipation zone thereon in the form of a bridge, as it is the case in the prior art, the invention provides an acoustic baffle produced as a whole from MU-metal sheet that is perforated in the area of the audio transducers and otherwise formed in a solid manner, or integrated in this area, whereby the radiation dissipation zone is formed in the perforated area of the MU-sheet metal in the form of one piece with this area. This embodiment of the acoustic baffle as defined by the invention offers the advantage that the acoustic baffle provides for even superior screening against radiation outside of the perforated area than a lattice structure coated with MU-metal. The one-piece embodiment comprising the acoustic baffle and the radiation dissipation zone provides the advantage that the manufacturing technique is substantially simplified as compared to low-radiation headphones of the prior art described above.
The net-like structure provided by perforating the MU-sheet metal exclusively in the area of the audio transducers may be embodied in a thickened manner for producing the radiation dissipation zone. However, this thickened area is preferably a perforation-free part of the otherwise perforated part of the MU-sheet metal forming the acoustic baffle.
Irrespective of its special embodiment, in which the radiation dissipation zone is extending in a tapered manner, as it is known per se, the radiation dissipation zone is formed so that it is the widest on the edge of the center of the perforated area, and the narrowest in the center of this area. In other words, the contour of the radiation dissipation zone accordingly extends in the form of a xe2x80x9cVxe2x80x9d. According to an advantageous further development of the invention, this radiation dissipation zone in the form of a bridge tapered in the direction of the center of the perforated area, is extended in a thickened manner beyond the perforated area up to the opposite peripheral edge of the MU-metal sheet forming the acoustic baffle. This relatively long bridge tapered to a point, provides for an optimized radiation dissipation zone as compared to the relatively short radiation dissipation zone extending from the center up to the edge of the perforated area of the MU-metal sheet forming the acoustic baffle, as explained above. A typical example of such a headphone is a small headphone resting against the ear.
Another typical example of the low-radiation headphone having the radiation dissipation zone as explained above is headphone that surrounds the ear. This headphone may be formed, for example as a headphone with front sound location. The preferably coaxial audio transducer system is for that purpose arranged out-of-center in the disk-shaped acoustic baffle, i.e. displaced to the front and downwards from a fictitiously central position in the acoustic baffle, viewed in the direction of sight of the headphone user. As a preferred form of embodiment of a low-radiation headphone with a coaxial audio transducer system in relation to its circular disk-shaped acoustic baffle for a front sound location of a sound event generated by such a converter system primarily in a small headphone resting against the ear, provision is advantageously made that a circular sector of the MU-metal sheet forming the acoustic baffle is formed from its circular edge up to the radial edges. Also in the area of the audio transducer system, partially covering the latter in a solid manner, i.e. in a non-perforated form, this circular sector containing the radiation dissipation zone, whereby the remaining acoustic baffle is perforated in the area of the audio transducer arrangement. The non-perforated area of the MU-metal sheet forming the acoustic baffle, and partly covering the coaxial audio transducer system is then located in the rear area of the respective headphone acoustic baffle in relation to a position of use of the headphone, for providing for optimal front sound location.
The solid circular sector of the MU-metal sheet forming the acoustic baffle is preferably a semicircular sector with an edge extending straight along its diameter. This semicircular sector also may have a solid area of the MU-metal sheet that is extended beyond its straight edge transversely in relation to the latter. The radiation dissipation zone is provided in this connection by the solid circular sector of the MU-metal sheet forming the acoustic baffle. In addition, the area may be structured to the extent that a bridge part extending to the rear at the top is additionally thickened, as with the headphone surrounding the ear as explained above.
Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings which disclose several embodiments of the present invention. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.
In the drawings, wherein similar reference characters denote similar elements. throughout the several views: